Regarding Ivanka’s conversion, if when she went into the mikva she intended to keep everything she is Jewish. That is halacha pesuka. As Rabbi Lookstein followed the RCA’s GPS there should not be a question.
Regarding going to the church, I heard that the prohibition is marit ayin. As the Kushners were conspicuously not holding prayer sheets and this was even noted by a reporter that might not be a problem. Moreover, Chazal relaxed the rules in this area for people who are karove lamalchut. Of course, the armchair poskim can say that one does not have to be karove lamalchut. They can even denigrate talmidei chachamim. However, they should remember a few things:
One who denigrates Torah scholars is defined as a heretic, who has no portion in the World to Come (Sanhedrin 99b).
Jerusalem was only destroyed because of denigration of Torah scholars (Rambam, Hilchos Talmud Torah, Chapter 6).
Anyone who denigrates a talmid chacham has no cure for his malady (Shabbos 119b) – and there are many different interpretations of exactly what that “malady” is.